Migraine headache is a common, recurrent, severe and often incapacitating condition estimated to affect 4-19% of adult men and 8-29% of adult women. One survey showed that severe headache is responsible for almost 10 million outpatient visits to physicians per year. The primary objectives of the proposed two-phase study are 1) to determine the prevalence of migraine, 2) to further refine the definition of a case of migraine and to characterize migraine subtypes 3) to identify important risk factors associated with the development and onset of migraine headaches in recent-onset cases in a community population and 4) to identify events which precipitate specific episodes of migraine headache among cases. These objectives will be accomplished by a study consisting of two phases. First, we will conduct a population-based prevalence survey in a well-characterized American community. Second, we will perform a case-control study using 220 recent-onset (incident) migraine cases identified in the prevalence survey. The proposed population-based prevalence study would be one of the first to be carried out in an American community; results could be compared to those from other population-based epidemiologic studies carried out in Great-Britain, Israel and Denmark. The methods used in the prevalence survey will provide a means to estimate the incidence of migraine. This would be unique in that we have been unable to find reports of any other incidence study. In the prevalence survey subjects who have had a recent attack of migraine will be asked about factors which may have precipitated the attack. In contrast to a number of past studies, this study will provide more reliable data on possible precipitants. Finally, a case-control study using recent-onset cases should allow us to focus on more specific hypotheses regarding risk factors suggested by previous work, including stress, psychosocial and personality factors; hormonal factors in women; and familial factors.